Chlorosulfonated polyethylene is a halogenated elastomer having no double bonds. Chloroprene rubber is also a halogenated elastomer, but chlorosulfonated polyethylene which is more resistant to heat, weather and ozone is regarded as a speciality elastomer that ranks above chloroprene rubber. Notwithstanding its superior characteristics, chlorosulfonated polyethylene has not gained as large a market share as chloroprene rubber. One reason for this limited commercial exploitation of chlorosulfonated polyethylene is that it is a difficult-to-process elastomer and that its processability is much inferior to that of chloroprene rubber. The following are major drawbacks encountered in processing chlorosulfonated polyethylene: (1) during mixing with an open roll mill, the rubber sticks to the rolls to reduce the operational efficiency; (2) the same problem occurs in making rubber coated fabrics with calender rolls and, in addition, air will be entrapped in the product to increase the reject rate of final products; and (3) after mixing in a Banbury mixer, the rubber compound cannot be readily recovered since it sticks to the rotor.
Under these circumstances, rubber processors who handle chlorosulfonated polyethylene usually improve its processability by means of addition of processing aids such as metal soaps (e.g., calcium stearate), polyhydric alcohols, low-molecular weight polyethylene, fatty acid esters and waxes. However, attempts to improve the processability of chlorosulfonated polyethylene by the agency of such additives have their own limits and abuse of these additives will cause undesirable phenomena such as blooming on the product surface and insufficient adhesion. Therefore, it has been desired to improve the processability of chlorosulfonated polyethylene not by the addition of chemicals but through the modification of the nature of the polymer itself.